In an image forming apparatus using a two component development method which uses toner and carrier, image defects, such as an image density and fog, occur when the life of a developer ends. On this account, when the life of developer ends, it is necessary to discharge the developer to exchange it for the new one.
For example, Japanese Laid-Open Utility Model Publication No. 71757/1989 (Jitsukaihei 1-71757, published on May 15, 1989) discloses a method for discharging the developer by (i) taking out a developing device from a main body, and then (ii) with a discharge opening of the developing device facing downward, rotating a coupling by hand or by external idling.
However, there are problems in that discharging and exchanging the developer is troublesome and take time. Specifically, for example, in a tandem color copying machine, the developing device has been miniaturized, so that it is difficult to discharge the developer.
Meanwhile, various image forming apparatuses including means for automatically discharging the developer have been proposed. For example, Japanese Unexamined Patent Publication No. 89061/1994 (Tokukaihei 6-89061, published on Mar. 29, 1994) discloses a technique of automatically discharging the developer by providing a discharging roller in addition to an agitating roller. In addition, this Tokukaihei 6-89061 also proposes a development apparatus including an automatic developer discharging means whose efficiency of discharging the developer is enhanced by increasing the size of the diameter of one conveying screw provided closer to the bottom of a developer tank than another conveying screw. Moreover, Japanese Unexamined Patent Publication No. 61958/2004 (Tokukai 2004-61958, published on Feb. 26, 2004) proposes an automatic developer discharging technique of automatically discharging the developer from the developing device and automatically injecting the new developer. Further, Japanese Unexamined Patent Publication No. 155460/2000 (Tokukai 2000-155460, published on Jun. 6, 2000) proposes a technology of (i) surely discharging the developer by detecting an output voltage of a toner concentration sensor when the developer is being discharged automatically and (ii) stabilizing the amount of the new developer injected.
However, in a conventional image forming apparatus (for example, a color tandem image forming apparatus) which includes a plurality of developer tanks for storing the developers, when discharging the developers, it is necessary to repeatedly carry out, for each developer tank, a process of (i) attaching to the developer tank a collecting container for collecting the developer and (ii) discharging the developer. This is low in work efficiency.
For example, in an image forming apparatus including a developer tank containing a K (black) developer, a developer tank containing a C (cyan) developer, a developer tank containing a M (magenta) developer, and a developer tank containing a Y (yellow) developer, in many cases, the cyan, magenta, and yellow developers are exchanged for the new ones at the same time. Since the operation of exchanging the developer is troublesome and takes time, it is done by a professional service person in many cases. In this case, the cyan, magenta, and yellow developers are usually exchanged at the same time. In this case, it is necessary to attach and detach the collecting container for each color, which lowers the work efficiency.
Moreover, when the developer is exchanged by the service person, the collecting container for the developer is usually prepared by the service person. However, in this case, it is necessary to prepare the collecting containers the number of which is equal to the number of the developer tanks. Since the collecting container is in the form of a box and voluminous, it is difficult for the service person to move with the collecting containers, and this leads to the low work efficiency.
Moreover, in the above-described conventional technology, there are problems in that it is difficult to completely discharge the developer and the developer remains at the bottom of the developer tank. For example, in the above-described Tokukaihei 6-89061, the efficiency of discharging the developer is enhanced by increasing the size of the diameter of one conveying screw provided closer to the bottom of the developer tank than another conveying screw.
However, in the case of providing the conveying screws in the developer tank, a certain gap (for example, 1 mm or more) is provided between the conveying screw and the developer tank to prevent pinching of the developer, etc. between the conveying screw and the developer tank. Therefore, it is not possible to discharge the developer remaining in the gap between the conveying screw and the developer tank. On this account, the developer remains in the developer tank in some cases. If the developer remaining in the developer tank is mixed with the new developer injected, the quality of the developer may deteriorate. Therefore, it is preferable to remove the developer remaining in the developer tank. In this case, in addition to a normal discharging operation, it is necessary to carry out an additional troublesome operation of removing the remaining developer. This is low in work efficiency.